[RFC] replace phputf8 with a maintained library

[HLeithner]

In Joomla 4 we have an indirect dependency of https://github.com/voku/portable-utf8 because of the php-stemmer we use.

Maybe it makes sense to consider this or any other library as alternative.

[nibra]

Replacing an outdated library totally makes sense. The consolidation of the tests (see #37) is the starting point.

[richard67]

See #55 .

[Hackwar]

Since there is the PR, I'm closing this one. Thanks @richard67 for reminding. 😉